Microfluidics deals with the behavior, precise control and manipulation of small volumes of fluids that are typically constrained to micrometer-length scale channels and to volumes typically in the sub-milliliter range. Prominent features of microfluidics originate from the peculiar behavior that liquids exhibit at the micrometer length scale. Flow of liquids in microfluidics is typically laminar. Volumes well below one nanoliter can be reached by fabricating structures with lateral dimensions in the micrometer range. Reactions that are limited at large scales (by diffusion of reactants) can be accelerated. Finally, parallel streams of liquids can possibly be accurately and reproducibility controlled, allowing for chemical reactions and gradients to be made at liquid/liquid and liquid/solid interfaces
More in detail, typical volumes of fluids in microfluidics range from 10−15 L to 10−5 L and are transported, circulated or more generally moved via microchannels with a typical diameter of 10−7 in to 10−4 m. At the rnicroscale, the behavior of fluids can differ from that at a larger, e.g., macroscopic, scale, such that surface tension, viscous energy dissipation and fluidic resistance may become dominant characteristics of the fluid flow. For instance, in microfluidics, the Reynolds number, which compares the effects of fluid momentum and viscosity, may decrease to such an extent that the flow behavior becomes laminar rather than turbulent.
In addition, at the microscale, fluids do not necessarily chaotically mix as at the microscale due to absence of turbulence in low Reynolds number flows, and interfacial transport of molecules or small particles between adjacent fluids often takes place through diffusion. As a consequence, certain chemical and physical fluid properties (such as concentration, pH, temperature and shear force) may become deterministic. This makes it possible to obtain more uniform chemical reaction conditions and higher grade products in single and multi-step reactions.
Microfluidic devices generally refer to microfabricated devices, which are used for pumping, sampling, mixing, analyzing and dosing liquids. A microfluidic probe is a device for depositing, retrieving, transporting, delivering, and/or removing liquids, in particular liquids containing chemical and/or biochemical substances. For example, microfluidic probes can be used in the fields of diagnostic medicine, pathology, pharmacology and various branches of analytical chemistry. Microfluidic probes can also be used for performing molecular biology procedures for enzymatic analysis, deoxyribonucleic acid (DNA) analysis and proteomics.
Retrieving substances from surfaces is important for numerous applications, e.g., in diagnostics, pharmaceutical and life science. When substances need to be recovered from different areas, this likely causes analytes to diffuse away from their initial recovery volume, which in turn causes cross-contaminations between sequentially recovered segments of liquid.